The present invention relates to power supplies and, more specifically, to a ferro-resonant transformer for an uninterruptible power supply.
Existing uninterruptible power supplies supply back-up alternating current to electronic components in the event of normal power in interruption. Such power supplies typically include a rechargeable battery, a rectifier circuit for providing a charging source to the battery and an inverter for producing alternating current from the battery. The transformers utilized within an uninterruptible power supply include windings for transforming normal service power to a load, auxiliary windings for battery charging, and windings for transforming battery-supplied alternating current to a load.
Typical uninterruptible power supplies utilize ferro-resonant transformers that are designed to operate exclusively with a specific battery type. In the field, uninterruptible power supplies generally use either 36 volt or 48 volt batteries. The batteries used depend upon the load to be driven by the power supply. An exemplary example of a prior art power supply can supply a 15 Amp output at 87 volts AC when used with a 36 volt battery. Another exemplary example of a prior art power supply with a different transformer, can supply a 22 amp output at 87 volts AC when used with a 48 volt battery source.
Customers often need to change from a 36 volt battery to a 48 volt battery if the load requirements of the system change. Thus, a different transformer must be used depending upon the voltage of the batteries installed in the system. Repair personnel who are charged with servicing and replacing defective power supplies and transformers and with modifying systems to meet changing needs must stock and transport at least two varieties of ferro-resonant transformers to accommodate the various battery types. Stocking and transporting the variety of ferro-resonant transformers increases the cost to the company and can become logistically difficult.
Therefore, there is a need in the art for an uninterruptible power supply that can operate with various types of batteries without requiring the transformer to be changed.
The present invention overcomes the above-described problems in the prior art by providing a power supply device, namely a transformer, for use with various types of batteries. The device operates with a single transformer and does not need to be matched to a certain battery type or voltage.
The transformer includes an average current loop circuit, a pulse width generator, a push-pull driver, and a pulse width modulator coupled to the average current loop circuit, the pulse width generator, and the push-pull driver for generating pulses for driving a power supply.
In a standard operating mode, the power supply is powered by an AC power source. The power supply uses the AC power source to drive the output of the power supply and to recharge the batteries associated with the power supply. When the power supply is operating on AC power, it translates the AC sinusoidal wave signal into a saw tooth wave signal that drives a pulse width modulator.
In an exemplary embodiment of the present invention, the duty cycle adjusts automatically based upon changes in the battery voltage and average battery current. This is done by monitoring the voltage and current loads on the power supply and determining a duty cycle setting that will meet the demands of the system.
Software inside the power supply monitors the pulses generated by the AC power source and replicates these pulses when the AC power source is interrupted. The software uses these pulses to synchronize the backup battery pulses with the AC pulses that regularly drive the system.
When the AC power source is restored, the software ensures that the pulses match those driven by the backup batteries. It is important that a clean hand-off occurs between the AC power source and the back-up batteries because it insures that the push-pull driver operates without interruption. In order to ensure that a clean hand-off occurs, the software and battery continue driving the power supply after AC power is restored until the software synchronizes the inverter to the AC power source input. Once the inverter and the AC power source arc synchronized, the AC power source resumes driving the system.
Other objects, features, and advantages of the present invention will become apparent upon reading the following derailed description of the embodiments of the invention, when taken in conjunction with the accompanying drawings and appended claims.